I don't have a clean reason for increasing the size of the cube. Doing so is pretty easy, it doesn't make it much harder to carry it around with me. I want more slots so that tweaking cards feels easier. It'll also smooth out some of the balance of the cube.
Most of the decisions for incoming cards were based on what slots were open in that color's curve.
WhiteAdanto Vanguard is a pet card of mine that works really well in aggressive strategies.
Sunset Revelry is a nice comeback card which is a mechanic I think the cube needs more of.
Austere Command is a board wipe that also hits non-creatures. The cube needed more board wipes.
Giant Killer this is a neat 1-drop that can function as a removal spell late game or a way to push damage in the early game.
Preordain is just a really solid one-drop. Not much to say.
Counterspell > Remand. With the adjustment to the mana base it became impossible to hold up counterspell on t2. Remand can be cast on t2 and serves as a way to snipe a good card from the queue.
Snapcaster Mage just a solid two-drop.
Shark Typhoon is a versatile card that can always be played on curve. The instant speed draw is also a huge boon.
Subtlety. I was having a hard time finding a good four drop that I liked. I wanted something versatile. Subtlety fits the bill as a counterspell and/or creature. Subtlety's evoke ability gets weaker in this environment.
Isareth the Awakener functions as a way to "cast" off-color spells that you ditched to the yard.
Spawn of Mayhem may be a bit too strong. It's very aggressive, but I'm hoping the self-ping makes it enough of a liability to keep it balanced.
Soulflayer is a fun card. There are enough haste and flying effects in the cube that it's definitely going to catch someone by surprise.
Thoughtseize probably should have been in the cube sooner. One of the issues I have had is lack of selection for removal. When a threat sticks you just have to be lucky. Hopefully thoughtseize can help keep things in check before they hit the battlefield.
Goblin Guide may be too strong. It will never draw your opponent cards. But I want to buff aggro, so we'll see if I went too far.
Kari Zev, Skyship Raider. Budget Ragavan? It's a good card that has relevant keywords for Soulflayer.
Abbot of Keral Keep is another strong two drop.
Seasoned Pyromancer is a solid three drop that can fuel graveyard shenanigans.
Green had a lot of changes made. I reworked the curve and made the color feel more cohesive than it did before.
Biogenic Ooze is good, but a pain to track. End-Raze Forerunners is a good chonker to ramp into that must be answered.
Beastmaster Ascension felt threatening, but never did anything. The card is either so good that it was kill on sight or so bad that it was never relevant. Realmwalker is going to be relevant even if it doesn't cast anything off the top.
Hexdrinker was terrifying, but probably not too busted; however, I wanted the slot to go to a mana dork. In comes Llanowar Elves.
Eskika's Chariot is really good, but it's not a creature itself. Master of the Wild Hunt, while not as aggressive, serves a similar purpose and is also removal.
Garruk Wildspeaker value, value, value. Helps ramp, puts bodies into play, serves as a win con if not answered.
Vivien's Arkbow this can serve as a way to clear the top of the library, can give you creatures outside of your colors, and as a decent mana sink.
Harmonize solid card to ramp into early or cast late in the game.
Chitterspitter solid token synergy. I also couldn't find a great 3 drop that I really liked.